The thermoelectric effect refers to phenomena by which either a temperature difference creates an electric potential or an electric potential creates a temperature difference. Thermoelectric materials show the thermoelectric effect in a strong or convenient form. Thermoelectric performance is defined by a dimensionless figure-of-merit ZT=(σS2T/κ), where σ is electrical conductivity (S m−1), S is the Seebeck coefficient (V K−1), and κ is thermal conductivity (W m−1K−1). Therefore, by going to much higher temperatures, ZT can be substantially increased. The power factor, PF=σS2, can be optimized by modifying the composition and crystallinity of the material. In particular, without a high degree of crystallization, ZT for thermoelectric materials tends to be unacceptably low due to deleterious effects to the power factor. Low-cost materials that have a sufficiently strong thermoelectric effect can be used in many applications, including power generation and refrigeration.
Metal oxide ceramics have recently garnered increased interest as thermoelectric materials for high-temperature energy harvesting applications. In particular, perovskites, including CaTiO3, SrTiO3, and BaTiO3 are interesting candidates for thermoelectrics because their electrical and thermal behavior can be tailored with A-site and B-site dopants. Further, the perovskites can accommodate multiple dopant atoms that can be used to reduce phonon heat transport while simultaneously creating defect states below conduction band.
However, a need remains to identify methodologies for reducing thermal conductivity without sacrificing thermopower and electrical conductivity of bulk oxides.